To meet the demand for wireless data traffic, which has increased since deployment of 4th-generation (4G) communication systems, efforts have been made to develop an improved 5th-generation (5G) or pre-5G communication system. Therefore, the 5G or pre-5G communication system is also called a ‘beyond 4G network’ or a ‘post long-term evolution (LTE) system’.
It is considered that the 5G communication system will be implemented in millimeter wave (mmWave) bands, e.g., 60 GHz bands, so as to accomplish higher data rates. To reduce propagation loss of radio waves and increase a transmission distance, a beam forming technique, a massive multiple-input multiple-output (MIMO) technique, a full dimensional MIMO (FD-MIMO) technique, an array antenna technique, an analog beam forming technique, and a large scale antenna technique are discussed in 5G communication systems.
In addition, in 5G communication systems, development for system network improvement is under way based on advanced small cells, cloud radio access networks (RANs), ultra-dense networks, a D2D communication, a wireless backhaul, a moving network, a cooperative communication, coordinated multi-points (CoMP), reception-end interference cancellation, and the like.
In the 5G system, a hybrid frequency shift keying (FSK) and quadrature amplitude modulation (QAM) modulation (FQAM) and a sliding window superposition coding (SWSC) as an advanced coding modulation (ACM) scheme, and a filter bank multi carrier (FBMC) scheme, a non-orthogonal multiple Access (NOMA) scheme, and a sparse code multiple access (SCMA) scheme as an advanced access technology have been developed.
Generally, a mobile communication system has a multi cell structure, and an interference control scheme in a multi cell mobile communication system is an important factor that affects total system performance of the multi cell mobile communication system.
So, various interference control schemes have been used in a current multi cell mobile communication system, typical interference control schemes are an interference alignment scheme and a time division/frequency division transmitting scheme, and each of the interference alignment scheme and the time division/frequency division transmitting scheme will be described below.
Firstly, the interference alignment scheme will be described with reference to FIG. 1.
FIG. 1 schematically illustrates an interference alignment scheme used in a general multi cell mobile communication system.
Referring to FIG. 1, the multi cell mobile communication system includes a plurality of base stations (BSs), e.g., three base stations, i.e., a base station #1 111, a base station #2 115, and a base station #3 113, and a plurality of user equipments (UEs), e.g., three UEs, i.e., a user equipment #1 117, a user equipment #2 121, and a user equipment #3 119.
In FIG. 1, a circle illustrated in each of the base station #1 111, the base station #2 115, and the base station #3 113 indicates an antenna dimension which may be used in a transmitter, and a circle illustrated in each of the user equipment #1 117, the user equipment #2 121, and the user equipment #3 119 indicates an antenna dimension which may be used in a receiver. That is, the base station #1 111, the base station #2 115, and the base station #3 113 are the first signal transmitting apparatus, the second signal transmitting apparatus, and the third signal transmitting apparatus, respectively, and the user equipment #1 117, the user equipment #2 121, and the user equipment #3 119 are signal receiving apparatuses which correspond to the first signal transmitting apparatus, the second signal transmitting apparatus, and the third signal transmitting apparatus, i.e., the first signal receiving apparatus, the second signal receiving apparatus, and the third signal receiving apparatus, respectively.
Further, w1, w2, and w3 indicate transmission signals which are transmitted by each of the signal transmitting apparatuses. In each of the signal receiving apparatuses, circles that are not hatched indicate an antenna dimension in which a main signal may be acquired, and hatched circles indicate an antenna dimension for processing aligned interference signals. Here, the interference alignment scheme denotes a scheme that a signal transmitting apparatus transmits a signal using a part of total antenna dimensions that the signal transmitting apparatus has thereby a signal is received in an interference alignment dimension in other signal receiving apparatus which is not a signal receiving apparatus which corresponds to the signal transmitting apparatus, i.e., a signal receiving apparatus that the signal transmitting apparatus interferes, and a signal is received in other antenna dimensions, not the interference alignment dimension in the signal receiving apparatus which corresponds to the signal transmitting apparatus.
That is, a signal transmitted by the base station #1 111 is received in a hatched circle, i.e., in an interference alignment dimension in the user equipment #2 121 and the user equipment #3 119, and is received in a circle which is not hatched, i.e., an antenna dimension which is not an interference alignment dimension in the user equipment #1 117. A signal transmitted by the base station #2 115 is received in an interference alignment dimension in the user equipment #1 117 and the user equipment #3 119, and is received in an antenna dimension which is not an interference alignment dimension in the user equipment #2 121. A signal transmitted by the base station #3 113 is received in an interference alignment dimension in the user equipment #1 117 and the user equipment #2 121, and is received in an antenna dimension which is not an interference alignment dimension in the user equipment #3 119.
Since there is no main signal which targets each of the signal receiving apparatuses, i.e., each of the user equipment #1 117, the user equipment #2 121, and the user equipment #3 119 in an interference alignment dimension, each of the user equipment #1 117, the user equipment #2 121, and the user equipment #3 119 may not decode signals received through the interference alignment dimension and decodes signals received through antenna dimensions except for the interference alignment dimension. Hereby, a corresponding signal receiving apparatus does not decode a signal received in an interference alignment dimension, so a signal received in remaining antenna dimensions except for an interference alignment dimension is not affected by interference.
An interference alignment scheme used in a general multi cell mobile communication system has been described with reference to FIG. 1, and a time division/frequency division transmitting scheme used in a general multi cell mobile communication system will be described with reference to FIG. 2.
FIG. 2 schematically illustrates a time division/frequency division transmitting scheme used in a general multi cell mobile communication system.
Prior to a description of FIG. 2, the time division/frequency division transmitting scheme is the most basic transmitting scheme that may remove influence of inter-cell interference in a multi cell environment, and total time/frequency resources which are usable in the multi cell mobile communication system are equally divided for K cells included in the multi cell mobile communication system, so the K cells independently use the divided time/frequency resources.
Signal transmission/reception in a case that K is 3 (K=3), i.e., a case that a time division/frequency division scheme is applied for three cells is illustrated in FIG. 2. In FIG. 2, each one indicates a base station and a user equipment which corresponds to the base station, and three types of hatched quadrangles with different forms indicate a time/frequency resource. If there are three cells in the multi cell mobile communication system, total time/frequency resource is equally divided into three parts, and each of the three cells uses one of the three parts thereby the three parts do not overlap one other.
A data rate which may be acquired by each of the three cells is ⅓ of a data rate in a case that each cell uses the total time/frequency resource of the multi cell mobile communication system, so there is loss in an aspect of data rate.
As described above, the interference alignment scheme has a problem that there is great loss for a remaining antenna dimension which is not used for signal transmission even though the interference alignment scheme may fully acquire a signal transmitted through an antenna dimension used for signal transmission without impact of other interference. The interference alignment scheme transmits a signal in a direction that interferences in other user equipments is aligned, not a direction that increases strength of a main signal on signal transmission, and an object of the interference alignment scheme is for acquiring a maximum degree of freedom, not a high data rate, so a data rate which is achieved when transmission power is low is not great.
In a case that transmission power is low, it may be difficult to guarantee that the interference alignment scheme which requires channel information related to all signal transmitting/receiving apparatuses has greater performance compared to other existing interference control schemes which do not require to acquire channel information. For performing the interference alignment scheme, all base stations need to be capable of using information on all interference channels included in an interference channel in real time. However, in a multi cell mobile communication system that channel characteristic changes in real time, it is difficult to correctly use channel information for all base stations in real time, and it is more difficult to carry correct channel information if there is capability limitations for a feedback link.
Further, the time division/frequency division transmitting scheme has an advantage that the time division/frequency division transmitting scheme does not require real-time interference channel information and may relatively easily transmit a signal without impact of interference. However, the time division/frequency division transmitting scheme has a disadvantage that acquirable data rate rapidly decreases in proportion to the number of base stations since a plurality of base stations divide and use the limited time/frequency resource. That is, due to impact of interference, a case that a few time/frequency resource is used may result in more serious loss to a data rate compared to a case that channel quality, e.g., a Signal-to-Interference plus Noise Ratio (SINR) decreases, so the time division/frequency division transmitting scheme generally has very low performance in a multi cell interference channel environment.
Further, there is a disadvantage that a user equipment does not use all of total transmission time when the multi cell mobile communication system uses the time division transmitting scheme, and there is a disadvantage that relatively narrow frequency band is used when the multi cell mobile communication system uses the frequency division transmitting scheme, so the user equipment is more seriously affected by channel state.
Recently, a mobile communication environment has become complex day by day, and has considered various base station environments as well as a hierarchical communication structure such as a femto-cell, and the like. So, a role of a base station becomes more important than ever for preventing performance degradation of a user equipment.
So, there is a need for an interference control scheme for considering various interference channel models for solving an inter-multi cell interference problem and decreasing amount of inter-cell interference.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present disclosure.